1. Biological soil crusts promote N accumulation in response to dew events in dryland soils
Manuel Delgado-Baquerizo; Fernando T. Maestre; Jesús G.P. Rodríguez & Antonio Gallardo. Soil Biology and Biochemistry (2013).

2. Introducction
In drylands, water is the most important factor limiting plant growth, net primary production and microbial decomposition (Austin et al. 2004; Schwinning and Sala 2004; Robertson and Groffman 2007)
In these ecosystems dew events may provide up to 40% of the water inputs received every year (from ~0.15 mm to ~ 0.30 mm per day; Kidron 2000; Jacobs et al., 2000; Moro et al., 2007; Lekouch et al., 2011)
However, not much is known about the influence that very small water pulses, such as those from dew events, have on biogeochemical cycles in drylands.

3. Introducction
Aranjuez experimental station (central Spain)

4. Introducction
N cycle in drylands
After water, nitrogen (N) is the main factor limiting
plant growth and decomposition in drylands (Schlesinger 1996)
Biocrusts, usually located in the open areas between plant canopies, largely modulate the N cycle in these ecosystems.

5. Other examples in: Belnap (2002), Zaady (2005) Su et al. (2011)
Introducction
Ex: 1 Increase total N and % of dissolved organic N regarding BS
Delgado-Baquerizo et al. 2010; Soil Biology and Biochemistry
Other examples in: Belnap (2002), Zaady (2005) Su et al. (2011)

6. Introducction Delgado-Baquerizo et al. (2013); Plant and Soil
Ex: 2 increase DON production in response to C, N and P addition regarding BS
Delgado-Baquerizo et al. (2013); Plant and Soil

7. Introducction
Ex: 3 more homogeneous soil conditions than plant canopies for Inorganic N
Delgado-Baquerizo et al. 2013; Journal of arid environments

8. G: ¿How biocrusts modulate the response of N availability to dew events in semiarid drylands?
H: Biocrusts will increase N availability in response to dew events

9. Methods Aranjuez experimental station (349 mm; 14.5 ºC).
Spring of 2010.
Twelve intact soil cores (5 cm depth, 7.5 cm diameter) were collected under each of two microsites: well-developed biocrusts and bare ground areas (BG)
Crust dominated by Diploschistes diacapsis

10. Methods
Air-dried soil cores with and without biocrusts (six replicates each) were incubated in a plant growth chamber for 14 days under two treatments: with and without (control) dew
Soil cores were incubated for 9 hours of light (20% RH, 20ºC) and 15 hours darkness (80% RH, 10ºC) simulating spring conditions in Aranjuez
In the dew treatment, soils were watered automatically three times during the darkness period to keep soil humidity constant at a 1% of SWC.
Before and after the experiment, we collected 2.5 g of soil (0-2 cm depth) from each replicated core.

11. Material y Métodos Ammonium Nitrate Dissolved organic N (DON)
Available N = Ammonium + Nitrate + DON
Amino acids
Carbohydrates= hexoses + pentoses
Phenols
Pentoses: hexoses -> proxy of origin from organic matter lichen vs. microorganisms
Carbohydrates: available N -> proxy of organic matter quality
We calculated the absolute increment in the values of each variable after 14 days of incubation (regarding initial concentrations).
Differences in the increment of these variables were evaluated using two-way ANOVAs: microsite & treatment

12. Results
Differences between treatments and microsites were not observed for either amino acids or nitrate (P > 0.05)

13. Results

14. available N for plant in their periods of activity
Discusion
Functional diversity and Fungal:bacterial ratio (Delgado-Baquerizo et al. 2013; Plant and soil)
DON & available N
available N for plant in their periods of activity
Dew pulses
Organic matter quality (lower labile C:N ratio)
available N

15. 80% of RH may active the N and C cycles in drylands
Discusión
Phenols production under biocrusts
Allelopathic effect on other groups of microorganisms from occupying a relative “N-rich” microsite
OM decomposition in response to a small water pulses (Austin et al. 2004).
Pentose: hexose ratio
Carbohydrates and N inmobilization under biocrust and BG for the control treatments
80% of RH may active the N and C cycles in drylands

16. Conclusions
We found that dew-like water inputs can promote the activation of microorganisms involved in the C and N cycles in dryland soils, and that this response is modulated by well developed biocrusts communities.
Biocrust increased the N availability in response to small pulses of water similar to dew events in semiarid ecosystems. Given the degree of development of BSCs in drylands worldwide, the high homogeneity of N cycle under biocrusts and the importance of water inputs from dew, the production of N under dew conditions can make an important contribution to the total N available for plants and microorganisms in these regions.
Biocrust increase the amount of soil phenols which may have a Allelopathic effect on other groups of microorganisms